Instrument to measure combustibles in liquid oxygen



Feb. 13, 1962 s. F. KAPFF ETAL 3,021,199

INSTRUMENT TO MEASURE COMBUSTIBLES IN LIQUID OXYGEN Filed Nov. 13, 19573 Sheets-Sheet 1 gar-W4 Jim 3 zwmgww a liar/1g Feb. 13, 1962 s. F. KAPFFEFAL 3,021,199

INSTRUMENT TO MEASURE COMBUSTIBLES IN LIQUID OXYGEN Filed Nov. 13, 19575 Sheets-Sheet 2 @4474 5201/ jzrwv'n/ 49m; mg 2M0. 9M

QW/cey Feb. 13, 1962 KAPFF ET AL 3,021,199

INSTRUMENT TO MEASURE COMBUSTIBLES IN LIQUID OXYGEN' Filed Nov. 13, 19573 Sheets-Sheet 5 6Q HRH/Y I v? Nf W 61 I 63 W F29 2 [Ma 67 .512? 69 PM i1 45 8 W FILL P0 WEE SUPPL Y Pl/HP RECORDER WSTRUWNT TU MEASURECOMBUSTIBLES EN LEQUID GXYGEN Sixt Frederick Kapfi, Homewood, and IrwinGinshurgh,

Chicago, Ill assignors to Standard Gil Company, Chicago, 111., acorporation of Indiana Filed Nov. 13, 1957, Ser. No. 696,252 6 Claims.(Ci. 23-230) This invention relates to method and means for accumulatingand monitoring the concentration of hydrocarbons in liquid oxygen oroxygen-rich liquid streams in liquid air plants.

The operation of plants for the production of pure oxygen or nitrogenfrom air basically involves a liquefaction of the air and subsequentfractionation of the components in a distillation tower. Thisdistillation is performed at low temperatures and produces an overheadproduct of pure nitrogen and a bottoms product of liquid oxygen. In theliquid oxygen will be found any substances present in the entering airwhich are not trapped out in the early cooling stages and have boilingpoints higher than oxygen. Some of the materials of interest are thehydrocarbons in the C C and 0.; range of molecular weights. The presenceof sizable quantities of these in the liquid oxygen presents a seriousexplosive hazard.

The safe operation of such a plant, therefore, involves maintaining thehydrocarbon concentrations as low as possible in the liquid oxygen. Theconcentrations considered tolerable vary for the different hydrocarbons.Acetylene is by far the most dangerous since in concentrations of a fewp.p.m. it reaches its solubility limit in liquid oxygen. The solidacetylene which then separates can detonate under certain conditionscausing serious explosions. The concentrations of other hydrocarbonsfrom ethylene to the butanes are not so critical since these are muchmore soluble in liquid oxygen. However, it is desirable to hold theirconcentrations as low as possible since, if any explosion should occur,these would furnish an additional fuel supply.

Monitoring the liquid air stream in the process is desirable for earlydetection of hydrocarbon concentration. An object of this invention is,therefore, to provide an instrument capable of measuring combustibles inliquid oxygen. A further object of the invention is to provide a methodand means whereby the hydrocarbon component can be concentrated forsubsequent detection and measurement. These and other objects of theinvention will become apparent as the description thereof proceeds.

Briefly, the instrument depends upon the adsorption of hydrocarbons fromgaseous oxygen stream (obtained by evaporation of liquid oxygen) uponcold silica gel, their subsequent desorption by heating, and theirdetection by combustion on a catalytic heated platinum wire. Cooling isprovided by contact with the liquid oxygen under test, the pressuregenerated providing the pumping necessary to drive the vaporized samplethrough the column. A Wheatstone bridge circuit including such platinumwire comprises the measurng means. Further details and advantages of ourinvention will be described by reference to a preferred embodimentillustrated in the accompanying drawings wherein:

FIGURE 1 is a diagrammatic illustration of one system, partly insection, of the hydrocarbon concentration cell;

FIGURES 2, 3 and 4 are views illustrating hydrocarbon detectorapparatus;

FIGURE 5 is a circuit diagram of the instrument; and

FIGURE 6 is a diagram of the detector bridge circuit 3,Zl,l% PatentedFeb. 13, 1962 employed with the detector apparatus of FIGURES 2, 3 and4.

Referring to the drawings, FIGURE 1 shows the details of therefrigerated vessel 10 having a cover 10:: and an air-tight gasket seal10b containing the silica gel adsorber 11. To analyze a liquid oxygensample, the operator pours the sample into the funnel 12 until liquid isobserved issuing from valve 13. He then presses start switch 31 (FIGURE5) and the instrument does the remainder of the operationsautomatically. The cartridge heater 15 turns on after the valves 13 and46 close and remains on as long as there is liquid oxygen present in thelower portion of the vessel 10 to keep the thermocouple 17 cold. Thegaseous oxygen and hydrocarbons which fill the upper part of the vessel10 enter inlet 16 and pass upwardly through the gel column 18 and theoxygen exhausts through line 58 and valve 19. When all the liquid oxygenhas been evaporated in vessel 10 and the thermocouple 17 begins to warmup, the cartridge heater 15 turns oif and theinstrument prepares to gothrough the desorption and analysis steps as described below.

In FIGURE 1, the column 18 comprises an annular gel bed 18a with glasswool distribution plugs 18b at the upper and lower ends of annularvessel 11. The top of the vessel is closed by cap ring 11b, lead gaskets11c and 11a providing necessary seals. Port 11e in cap ring 1112 permitsfree access of the refrigerating gas through and about the annularvessel.

The adsorbed hydrocarbons are desorbed from column 18 into anoxygen-containing carrier gas stream 20 and detected with a catalyticplatinum wire detector 21 similar to that shown in FIGURES 2, 3 and 4.The platinum wires 22 and 23 are connected in the bridge circuit shownin FIGURE 6. A selector switch 25 permits operation of the recorder 26at two sensitivties to cover a wide range of hydrocarbon concentrations.

The calibration of this instrument depends upon the catalytic activityof the platinum wires 22 and 23 used as detectors. Since these changetheir activity from time to time, it is necessary to supply a standardsignal to check them. This is done by permitting a small quantity ofcombustible gas to enter the oxygen stream 20 passing to the detectors21. It has been found that a flow of 2.9 cc. of ethylene per minute intothe oxygen stream 20 flowing at 0.10 c.f.m. gives a recorder signalcorresponding to that obtained from 6 ppm. of hydrocarbon in a liquidoxygen sample. This standardization occurs during every determinationand all concentrations are calculated relative to it.

A cylinder 27 of dry gas, such as gaseous ovygen, is connected to thisinstrument and provides a gas flow for three purposes: (1) During thetime when the liquid oxygen is being evaporated, the cylinder gas ispumped through the detecting cell 21, thus permitting the bridge currentand zero to be adjusted and a good zero to be obtained. (2) During thedesorption period when the pump 28 is pulling gas from the refrigeratedvessel 10 through the gel column 18, the dry cylinder gas flow passesthrough the refrigerated vessel 10 to protect against the entrance ofhumid room air which in this cold system would soon cause ice blockage.(3) The third function of the cylinder gas is to serve to flush out therefrigerated vessel 10 after a sample containing high concentrations ofhydrocarbons has been run.

Before starting any test, the device is connected to gaseous oxygencylinder 27 through reducing valve 32 and to standardizing gas(ethylene) cylinder 27a through reducing valve 34 which is adjusted to10 p.s.i.g.

If instrument has not been used for a period of several hours, flushswitch 29 is placed in the "flush position. This energizes valves 13 and45 causing gaseous oxygen from cylinder 27 to pass through vessel 10,sweeping out any moisture which may have diifused in as well as anyresidual hydrocarbon vapors from previous tests. The range switch 25 isset for high or low concentration. Switch 29 is returned to the runposition closing valve 45 and switch 31 is placed in the fill position.This opens valves 46 and 13 so that sample liquid may be poured throughfunnel 12 to a level determined by outlet conduit 47. When liquid isseen to issue from valve 13, the instrument is ready to begin a test.

Switch 31 is placed in the start position. This closes valves 46 and 13and opens valve 48. Switch 31 is a spring-return type and remains instart only momentarily. At the same time, relay 49 is reset by coil 50opening switch 51. Relay 52 (used as a time-delay relay) actuates aboutone second after relay 4-9 has been reset and provides power to contactsof switch 51. At the same time, power is supplied by self-locking relay54 to pilot light 66, pump 28, and to the power supply for the detectingand recorder circuits of FIGURE 6.

Thermal delay relay 53 is energized through relay 54, relay 53 providingcurrent to the motor of recorder 26 when energized. A delay of 60seconds in relay 53 is used to reduce the large recorder deflectionsometimes obtained while the recorder and detector circuits are warmingup.

By relay 54- power is supplied to cartridge heater '15 which heats andevaporates the liquid oxygen sample in vessel 10. During thisevaporation, the operator set the flow through pump 2% by adjustingvalve 32 and observing flow meter 33. The detecting bridge current andrecorder zero are also set at this time. The bridge current is set at0.60 ampere and the zero of recorder 26 is adjusted by zero adjusthelipot 35 in FIGURE 6.

When evaporation of the liquid oxygen sample has been substantiallycompleted, thermocouple 17 in vessel 10, being no longer immersed incold liquid, heats up and actuates relay 49. This removes power from thecartridge heater 1S and normally closed valve 48 by means of relay 55.At the same time, (a) the timer motor 56 is started by the action ofcoil 57 and switch 66; (b) valves 45 and 13 (by action of switch 64) areopened, permitting a stream of gaseous oxygen from cylinder 27 to passthrough the vessel and (c) valve 19 is energized to connect pump 28 toline 58, thus drawing gas through the gel column 18.

Closing of timer switch 59 actuates pilot light 67 and opens valve 42permitting standardizing gas from cylinder 27a to enter the oxygenstream flowing in line 20 through the high resistance leak 60 to checkthe detector 21. Switch 59 then opens. Referring to FIGURE 5, timerswitch 61 is next actuated by the action of the timer to provide powerto transformer 62 and pilot light 68, the secondary of which isconnected to gel heater 63. Resistance 69 in the primary circuit of thetransformer 62 is chosen to provide the proper heating current to gelheater 63 via leads from the kovar seals 100 in cover 10a.

At the completion of the preset time for desorption of the adsorbedhydrocarbons, timer switch 65 operates to de-energize relay '54. Timerswitch 65 returns to the closed position just before switch 66 opensending the test.

When the pilot light 66 goes out, the test has been completed and thehydrocarbon concentration can be calculated from the ratio of the heightof the desorb peak to the standardizing peak of 6 p.p.m. on a chartrecord. If the sample has shown a hydrocarbon concentration greater thanp.p.m., the flush switch 29 is held in the flush position for at leastthree minutes. This clears out any remnants of the previous sample andprepares the instrument for another test.

In summary, the timer starts after the liquid oxygen has all evaporatedin 10 and has the following sequence:

(1) The cylinder oxygen from 27 is diverted to the refrigerated vessel19 and the pump 28 is opened to the outlet of the gel column 11;

(2) The standardizing gas valve 42 is opened to check the activity ofthe platinum filaments 22 and 23 and to provide a reference signal; and

(3) The gel column 11 is heated to desorb any adsorbed hydrocarbons. Thetimer then turns oif and the test is concluded.

Samples of liquid oxygen containing known concentrations of hydrocarbonswere prepared and used to standardize the instrument. Our technique hasbeen to fill a small 1.6 cc.) gelatin capsule with hydrocarbon gas bymeans of a hypodermic syringe. This capsule is then immersed in liquidoxygen. After the capsule has come to liquid oxygen temperature, it isbroken beneath the surface of the liquid, the hydrocarbon gas dissolvingV in the liquid oxygen quantitatively.

The calibration with different hydrocarbons shows some instrumentsensitivity to hydrocarbon type. For example, for a given hydrocarbonconcentration, the instrument will give about twice as large a signalfor ethylene as for ethane. This may be a unique property of the Ussince propane and propylene give essentially the same instrumentresponse.

It has been found that if the gel column 18 is heated gradually, thevarious hydrocarbons adsorbed thereon will desorb at characteristictemperatures. This gradual heating may be accomplished, for example, byinserting between switch 61 and gel heater 63, by means of a steppingrel y, suitable resistances in predetermined sequence to vary thecurrent flowing in heater 63. Hence calibration with known gases willpermit qualitative and quantitative estimation of the gases adsorbed.

If an analysis of the gas being desorbed from a gel is desired, theoutput of the detector 21 is plotted on one axis of an X-Y recorder withthe other axis representing the temperature of the silica gel column.The record so obtained indicates hydrocarbon concentrationas a functionof the temperature of desorption.

It is contemplated that adsorbents other than silica gel may be usedincluding molecular sieve-type adsorbents, activated carbon and alumina,and the like. A double column system may be used in series for theadsorption and in parallel for desorption. Thus molecular sievetypeadsorbents may be used to accumulate methane after the C -C hydrocarbonshave been retained by the silica gel column. suitably programmed and twodesorption signals shown on the recorder.

The invention has been described in terms of a system for concentratingdilute hydrocarbons from oxygen-rich streams. The invention has furtherbeen described in connection with a detector for the concentratedhydrocarbons comprising a device wherein they are oxidized. However, insome circumstances it may be desirable to preserve the hydrocarboncomponents and the detector may comprise non-destructive detectors, suchas thermal conductivity cells, gas gravity balances, chromatographicanalyzers, and the like. of the hydrocarbons as taught makes possiblethe use of rugged and less sensitive detectors and makes unnecessaryexpensive apparatus utilizing techniques such as involved in massspectrometers, infrared analyzers, and the like.

Although the invention has been described With reference to embodimentsthereof, it should be understood that these are by way of illustrationonly and that the invention is not necessarily limited to suchembodiments. Alternative components and operating techniques will becomeapparent to those skilled in the art in view of the foregoing disclosureand, accordingly, modifications in the construction and operation of theapparatus are contemplated without departing from the spirit of theinvention.

The desorption of the two columns may be In any event, the concentrationWhat we claim is:

1. An apparatus for analyzing liquid oxygen for its hydrocarbon contentwhich comprises chamber means for vaporizing a quantity of a sample ofoxygen-rich liquid, adsorption means in said chamber means and incommunication therewith for selectively adsorbing vaporizedhydrocarbons, means for cooling said adsorption means by said liquidsample in heat exchange therewith, means for flowing a stream of gaseousoxygen into said chamber means and through said apparatus,temperature-responsive means responsive to the temperature in saidchamber adapted to control said means for flowing said stream of gaseousoxygen, means for heating said adsorption means to desorb said adsorbedhydrocarbons into said stream, and hydrocarbon detector means includinga catalytic element adapted to effect combustion of said desorbedhydrocarbons and thereby indicate the concentration of hydrocarbons insaid flowing stream.

2. An apparatus for monitoring small quantities of dissolvedhydrocarbons in an oxygen-rich liquid sample comprising in combination avaporizing chamber, means for supplying said sample to said chamber, acolumn of an adsorbent mass in said chamber cooled by said sample, saidcolumn being in communication with said chamber, conduit means forflowing a gasiform sample stream into said chamber and through saidcolumn, means for heating said column periodically to desorbhydrocarbons therefrom, means for flowing gaseous oxygen through saidapparatus to sweep the desorbed hydrocarbons from the said column, anddetector means including a catalytic element adapted to effectcombustion of said desorbed hydrocarbons in said flowing gaseous oxygen,the combustion being a measure of the concentration of hydrocarbons insaid oxygen-rich liquid sample.

3. An apparatus for analyzing an oxygen-rich liquid sample for smallconcentrations of hydrocarbons which comprises adsorption column meansfor accumulating the hydrocarbons, chamber means for vaporizing a liquidsample in heat exchange with said adsorption column means, one end ofsaid adsorption column means being open to the interior of said chambermeans, means for sensing when vaporization of the sample is complete,means for flowing gaseous oxygen from a separate source into saidchamber means and through said adsorption column means at a uniform ratewhen such vaporization has taken place, means for heating the saidadsorption means to desorb hydrocarbons therefrom, and means including acatalytic element for effecting combustion of said desorbed hydrocarbonsto indicate the concentration of hydrocarbons in said flowing gaseousoxygen stream as a measure of the concentration of hydrocarbons in saidliquid oxygen sample.

4. The apparatus of claim 3 wherein the adsorption means contains silicagel, said chamber means is a Dewar vacuum flask, and the means foreffecting the combustion of hydrocarbons includes a heated platinumfilament in a bridge circuit.

5. A method for monitoring the concentration of hydrocarbons in liquidoxygen-rich streams flowing in air liquefaction plants which comprisesvaporizing a sample of such liquid oxygen within a confined space toproduce a gasiform stream of gaseous oxygen and hydrocarbon vapors,flowing the gasiform stream through an adsorption zone, maintaining saidzone at a low temperature by heat exchange contact with the liquidsample and said gasiform stream, separating hydrocarbons from saidstream in said adsorption zone, heating said zone to desorb the adsorbedhydrocarbons, simultaneously with said heating flowing a stream ofgaseous oxygen through said zone as a sweep gas, and effectingcombustion of the desorbed hydrocarbons in said gaseous oxygen on acombustion-catalyzing element, said combustion being a measure of theconcentration of hydrocarbons in said liquid oxygen-rich streams.

6. An apparatus for monitoring an oxygen-rich stream containingdissolved hydrocarbons comprising thermally insulated vessel means,column means in said vessel for concentrating said hydrocarbons, saidcolumn means having an inlet in communication with said vessel, meansfor vaporizing a sample of such stream in said vessel, conduit means forflowing said vaporized sample through said column, control means withinsaid vessel responsive to the complete vaporization of said sample,means for heating the said column means to liberate the hydrocarbonstherefrom, said control means actuating said heating means, means forflowing an oxygen carrier gas through said vessel and said column meansto sweep the concentrated hydrocarbons from said vessel, and a catalyticplatinum filament in a bridge circuit adapted to effect combustion ofsaid hydrocarbons in said oxygen carrier gas and detect such combustionas a measure of the hydrocarbon content of said oxygen-rich stream.

References Cited in the file of this patent UNITED STATES PATENTS2,398,818 Turner Apr. 23, 1946 2,429,555 Langford et al Oct. 21, 19472,826,908 Skarstrom Mar. 18, 1958 OTHER REFERENCES Gas Chromatography inPlant Streams, by D. H. Fuller, in ISA Journal, November 1956, pages440-444.

Chromatographic Analysis of Hydrocarbon Mixtures, by Bradford et al., inJournal of Institute of Petroleum, vol. 41, 1955, pages -88.

Book, Vapor Phase Chromatography, Desty. Butterworth ScientificPublications, London, 1956, page 215. (Article by Drew et al.)

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,021,199 February 13, 1962 Sixt Frederick Kapff et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 61, for "measurng" read f-- measuring column 2,v line 51,for "'ovygen'= read oxygen column 4, line 23, for "C's": read C s Signedand sealed this 3rd day of July 1962.

(SEAL) Attest:

DAVID L. LADD Commissioner of Patents ERNEST W. SWIDER Attesting Officer

5. A METHOD FOR MONOITORING THE CONCENTRATION OF HYDROCARBONS IN LIQUIDOXYGEN-RICH STREAMS FLOWING IN AIR LIQUEFACTION PLANTS WHICH COMPRISESVAPORIZING A SAMPLE OF SUCH LIQUID OXYGEN WITHIN A CONDINED SPACE TOPRODUCE A GASIFORM STREAM OF GASEOUS STREAM THROUGH AN ADSORPVAPORS,FLOWING THE GASIFORM STREAM THROUGH AN ABSORPTION ZONE, MAINTIANING SAIDZONE AT A LOW TEMPERATURE BY HEAT EXCHANGE CONTACT WITH THE LIQUIDSAMPLE AND SAID GASIFORM STREAM, SEPARATING HYDROCARBONS FROM SAIDSTREAM IN SAID ADSORPTION ZONE, HEATING SAID ZONE TO DESORB THE ADSORBEDHYDROCARBONS, SIMULTANEOUSLY WITH SAID HEATING FLOWING A STREAM OFGASEOUS OXYGEN THROUGH SAID ZONE AS A SWEEP GAS, AND EFFECTINGCOMBUSTION BEING A MEASURE SORBED HYDROCARBONS IN SAID GASEOUS OXYGEN ONA COMBUSTION-CATALYZING ELEMENT, SAID COMBUSTION BEING A MEASURE OF THECONCENTRATION OF HYDROCARBONS IN SAID LIQUID OXYGEN-RICH STREAM.